The invention is directed to a process for production of sorbents based on smectite for the uptake of liquids. These sorbents are suitable for taking up any desired liquids; however, they are especially good as pet litter.
The keeping of pets in a largely urbanized environment is increasingly dependent on the use of litter materials. The task of these materials is to absorb the fluids given off by the animals and to suppress or prevent the development of odor if possible. Moreover, they are required to remove moisture from the semisolid, moist animal excrement and excretions, in order to reduce the development of odor. Good litter materials, furthermore, have the property of taking up the excreted or removed fluids by forming a compact clump, which can be removed in a simple and economical way. Therefore, an optimal animal litter has a high absorption capacity.
The products that can be found on the market include organic substances such as straw, sawdust, wood shavings, bark, porous synthetic beads, shredded paper, cellulose fibers, agricultural wastes, polyacrylates, etc. These are used by themselves or in mixtures with inorganic materials. The disadvantage of the organic litter materials is an often unsatisfactory clumping or consistency of the clump, as well as their tendency to bacterial decomposition, especially in conjunction with moisture.
German Patent No. 3,836,345 discloses an animal litter comprised of granular, porous absorbing material. The preferred material consists primarily of calcium silicate hydrate, e.g. cellular concrete, treated with an antimicrobial substance which is a nonhalogenated aromatic hydrocarbon to hinder the occurrence of unpleasant odors. Smectite clay materials are not disclosed.
German Patent No. 3,825,905 discloses a mineral substance to soak up toxic liquids, emulsions and/or suspensions. The mineral substance consists of clay minerals selected from kaolinite, illite, sericite and/or smectite which are roasted at temperatures above 650.degree. C. These materials have an open porosity of at least about 30 vol. percent and a mean pore size of between 0.05 and 500 microns. A treatment to enhance the water uptake capacity of these products is not possible because of the highly roasted nature of the clay minerals.
European Patent No. 087,001 corresponding to U.S. Pat. Nos. 4,591,581 and 4,657,881 disclose absorbent materials comprised of clay mineral particles in the size range of about 710 microns to 4 millimeters consisting of compacted masses of small clay particles of a size less than about 2 millimeters. The clay particles are preferably smectite, attapulgite or sepiolite. No information is provided on improving the water uptake capacity by kneading the materials in their moist state.
There are also bentonite-based litter materials, as disclosed in U.S. Pat. Nos. 5,000,115, 4,657,881, 5,000,115, and 5,129,365, for example, which have certain advantages over the organic litters. Through their ability to swell with aqueous liquids, the bentonites are capable of forming clumps. Because of this clumping, the portion of the litter wetted by the fluid can be removed separately, thus economizing on litter. The special structure of the bentonites is also responsible for their ability to adsorb unpleasant odors produced by the animal's excretions and excrement. Disposal of bentonites, furthermore, is not a burden on the environment.
According to the above-mentioned state of the art, sodium bentonites or mixtures of sodium bentonites and calcium bentonites are used as sorbents, e.g., litter material for pets. These sorbents can be used in granulated form.
However, these are only mechanical mixtures, whose water uptake ability represents the arithmetic mean of the water uptake abilities of the individual components.
Now, surprisingly, it has been found that the water uptake capacity of such mixtures can be substantially improved if the ingredients are chemically reacted with each other under certain conditions.